Injection button

ABSTRACT

A push button connection for an injection device comprising a push button ( 10 ) and a driving part ( 20 ). The two parts of the push button connection are mounted to each other and is relatively rotatable to each other. In order to minimize the friction occurring between the push button and the driving part when relatively rotated forces are transmitted via a pivot bearing ( 18, 22 ). In order also to minimize the effect of forces appearing dislocated from the center line a number of radial bearings ( 13, 23; 14, 25 ) having a little friction diameter is provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. §371 national stage application ofInternational Patent Application PCT/EP2008/050624 (published asWO2008/095762), filed Jan. 21, 2008, which claimed priority of EuropeanPatent Application 07101729.7, filed Feb. 5, 2007; this applicationfurther claims priority under 35 U.S.C. §119 of U.S. ProvisionalApplication 60/899,977, filed Feb. 7, 2007.

THE TECHNICAL FIELD OF THE INVENTION

The invention relates to a push button connection for an injectiondevice and especially to such connection where a push button is rotatedrelatively to a driving member to which it is connected.

DESCRIPTION OF RELATED ART

U.S. Pat. No. 6,235,004 discloses an injection device in which accordingto FIG. 15-16 a dose is set by rotating the scale drum out of thehousing in a threaded connection. When injecting the set dose the userpushes on the push button which forces the scale drum and the bushing torotate together back into the housing. During this rotation of thebushing to which the push button is attached, the push button and thebushing rotates relatively to each other. The friction occurring betweenthese relatively rotatable parts contributes to the force a user needsto apply in order to push back the bushing and the scale drum in orderto inject the set dose.

U.S. Pat. No. 7,427,275 discloses an injection device in which the pushbutton is formed with a bore encompassing a stem on a sleeve member. Thepush button and the stem are welded together such that the push buttonand the sleeve member are axially and rotatably fixed to each other.

DESCRIPTION OF THE INVENTION

It is an object of the present invention to provide a dose buttonconnection for an injection device which minimizes the forces a usermust apply to inject a dose.

When a user pushes on the injection button, the force applied isdirected to the forward movement of the driving part, however, since thepush button and the driving part rotate relatively to each other afriction between these rotating parts will occur. The user thereforealso has to apply a force large enough to overcome this friction. Oneway of minimizing the force a user must apply in order to perform aninjection is therefore to minimize this friction. By forming a pivotbearing between the two parts, the surface area of interaction betweenthe two objects can be minimized and the radius of the resultingfriction force can be kept at a minimum.

In order to secure the fit between the push button and the driving partand on the same time direct forces applied on the periphery of the pushbutton to the driving part at least one radial bearing between the pushbutton and the protrusion is formed.

Preferably one radial bearing is formed in the upper area and one isformed in the lower area both having the least possible radius offriction. In this way forces applied at in the periphery area of thepush button and causing tilting of the push button on the protrusion ofthe driving part is properly transferred.

If a user applies a force eccentric to the centre axis of the pushbutton i.e. on a peripheral area of the button, the push button willtilt and a reaction torque will occur at the radial bearings. In orderto minimize this force pair, which in this load case is located at thedistance from the radial bearing surface to the centre axis of thesystem, this distance, which again equals the radius of the protrusion,must be as little as possible and the distance between the bearings aslong as possible. However, in order not to make the protrusion toonarrow and fragile it is preferred to balance the radius of thebearings, such that the upper bearing has the smallest diameter and thelower bearing at the root of the column shaped protrusion has a diameterlarge enough to resist the bending force as a result of the offsetapplied push button forces.

In order to assemble the push button in an irreversible manner making itdifficult to dissemble, it is preferred to secure the push button at theintended position by adding a track into which a rim on the harder partis forced during the manufacture of the injection device. The necessarycompliance of the push button for the assembly snap-on can be secured byselection of a soft material and/or a vertical slit in the hollowsection of the geometry.

Further the materials used for the push button and the protrusion on thedriving part could be materials having low internal friction, or thematerials could be surface treated in order to lower the internalfriction.

The push button used in the connection has a central bore dedicated toengage the protrusion provided on the driving part. The bottom of thebore is preferable formed with a pivot. This pivot bears on a surface ofthe protrusion thus forming a pivot bearing.

DEFINITIONS

An “injection pen” is typically an injection apparatus having an oblongor elongated shape somewhat like a pen for writing. Although such pensusually have a tubular cross-section, they could easily have a differentcross-section such as triangular, rectangular or square or any variationaround these geometries.

As used herein, the term “drug” is meant to encompass anydrug-containing flowable medicine capable of being passed through adelivery means such as a hollow needle in a controlled manner, such as aliquid, solution, gel or fine suspension. Representative drugs includespharmaceuticals such as peptides, proteins (e.g. insulin, insulinanalogues and C-peptide), and hormones, biologically derived or activeagents, hormonal and gene based agents, nutritional formulas and othersubstances in both solid (dispensed) or liquid form.

All references, including publications, patent applications, andpatents, cited herein are incorporated by reference in their entiretyand to the same extent as if each reference were individually andspecifically indicated to be incorporated by reference and were setforth in its entirety herein.

All headings and sub-headings are used herein for convenience only andshould not be constructed as limiting the invention in any way.

The use of any and all examples, or exemplary language (e.g. such as)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention. The citation and incorporation of patent documents hereinis done for convenience only and does not reflect any view of thevalidity, patentability, and/or enforceability of such patent documents.

This invention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained more fully below in connection with apreferred embodiment and with reference to the drawings in which:

FIG. 1 Show a cross section view of the connection between a push buttonand a driving part.

FIG. 2 Show a cross section view of the connection and the forcesoccurring.

The figures are schematic and simplified for clarity, and they just showdetails, which are essential to the understanding of the invention,while other details are left out. Throughout, the same referencenumerals are used for identical or corresponding parts.

DETAILED DESCRIPTION OF EMBODIMENT

When in the following terms as “upper” and “lower”, “right” and “left”,“horizontal” and “vertical”, “clockwise” and “counter clockwise” orsimilar relative expressions are used, these only refer to the appendedfigures and not to an actual situation of use. The shown figures areschematic representations for which reason the configuration of thedifferent structures as well as there relative dimensions are intendedto serve illustrative purposes only.

In that context it may be convenient to define that the term “distalend” in the appended figures is meant to refer to the end of theinjection device carrying the injection needle whereas the term“proximal end” is meant to refer to the opposite end pointing away fromthe injection needle.

FIG. 1 discloses the connection between the push button 10 and thedriving part 20.

When a user wants to inject a dose, which he or she has first selected,the user pushes the push button 10 which then moves the driving part 20axially forward in the injection device. During this forward movement ofthe driving part 20 it also rotates usually because it is interfacedwith a dose dial drum which is threadedly connected to a housing. Suchinjection device is described in details in EP 1.003.581. The combinedaxial and rotatable movement of the driving part 20 drives the set doseout from the injection device.

As the users finger pushes on the push surface 11 of the push button 10it is unable to rotate due to the friction between the users finger andthe push button 10 whereas the driving part 20 is forced to rotate dueto its interface, therefore a relative rotation between the push button10 and the driving part 20 takes place.

The push button 10 which could be manufactured from a suitable polymericmaterial being softer that the material from which the driving part 20is manufactured comprises at the proximal end a push surface 11 which iscontacted by the user's finger when a dose is to be injected and anopposite located cylindrical bore 12 with a circular cross section. Themost proximal part 13 of the bore 12 has a smaller diameter than theremaining part 14 of the bore 12. At the distal end of the bore 12, aradial extending track 15 is provided.

The push surface 11 could be provided with a tactile cut-out 16informing visual impaired users on the content of the injection deviceand the most proximal bottom surface 17 of the bore 12 is formed with araised pointer forming a pivot 18.

The driving part 20 is provided with a protrusion 21 having a circularcross section and a top surface 22. This protrusion 21 has at itsproximal end a top part 23 with a decreased diameter compared to theremaining part 26 of the protrusion 21. Further the protrusion 21 isprovided with a radial extending rim 24 at its distal end. In the areaaround this rim 24, the protrusion 21 is provided with a belt 25 with aslightly raised diameter.

When the push button 10 is mounted on the protrusion 21 of the drivingelement 20 it is simply clicked on such that the extending rim 24 entersthe track 15. This forms a connection almost impossible to disconnectsince the polymeric material of the push button 10 is softer than thematerial from which the protrusion 21 is produced. In this position thepivot 18 formed in the most proximal bottom surface 17 of the bore 12bears on the top surface 22 of the protrusion 21 thus forming a pivotbearing 22, 18. Further the push button 10 is radially supported by theprotrusion 21 at the top part 23 forming a radial top bearing 23, 13.The belt 25 on the protrusion 21 bears on an area of the remaining part14 of the bore 12 thus forming a radial bottom bearing 14, 25.

In FIG. 2 the push button 10 connection is disclosed with the variousforces occurring when a user applies an injection force in theperipheral area of the push button 10.

When the user applies an injection force A at the peripheral area of thepush button 10 a vertical reaction force B will appear at the pivotpoint 22, 18, at the same time a radial force C will occur at the upperradial bearing 13, 23. Since the upper radial bearing 13, 23 are locatedat the top part 23 having the smaller diameter, the resulting torque isrelatively small. Further, a radial force D will occur at the lowerradial bearing 14, 25, however due to the distance between the upperradial bearing 13, 23 and the lower radial bearing 14, 25, the forceresulting on the lower radial bearing 14, 25 is relatively small.

Some preferred embodiments have been shown in the foregoing, but itshould be stressed that the invention is not limited to these, but maybe embodied in other ways within the subject matter defined in thefollowing claims.

The invention claimed is:
 1. A push button connection for an injection device comprising: a push button mountable on a driving part being rotatable relatively to the push button and which push button further comprises a bore with a bottom surface and which bore surrounds a protrusion on the driving part which protrusion has a top surface and wherein a pivot bearing is formed between the bottom surface and the top surface, wherein when a user presses on the push button the force is directed toward the driving part and wherein the driving part rotates relative to the push button.
 2. A push button connection according to claim 1, in which at least one radial bearing between the push button and the driving part is provided.
 3. A push button connection according to claim 2, in which an upper radial bearing is provided at a top part of the protrusion and a lower radial bearing is provided at the bottom of the protrusion.
 4. A push button connection according to claim 3, in which the top part of the protrusion accommodating the upper radial bearing has a diameter smaller than the diameter of the remaining part of the protrusion.
 5. A push button connection according to claim 1, in which the push button is manufactured from a polymeric material being softer than the material from which the driving part is manufactured.
 6. A push button connection according to claim 1, in which the protrusion is provided with an extending rim mating with a track provided in the push button. 